Critical point Higgs inflation in the Palatini formulation

TL;DR

This paper investigates Higgs inflation within the Palatini formulation, analyzing how loop-induced features and threshold corrections affect inflationary predictions, including spectral index and tensor-to-scalar ratio, with implications for distinguishability from metric formulations.

Contribution

It introduces a detailed analysis of Higgs inflation in the Palatini framework considering quantum corrections and threshold effects, highlighting differences from metric formulations.

Findings

Spectral index can vary within observational bounds.

Tensor-to-scalar ratio is extremely small, between 2.2×10⁻¹⁷ and 2×10⁻⁵.

Quantum corrections do not erase differences from metric formulation.

Abstract

We study Higgs inflation in the Palatini formulation with the renormalisation group improved potential in the case when loop corrections generate a feature similar to an inflection point. Assuming that there is a threshold correction for the Higgs quartic coupling $\lambda$ and the top Yukawa coupling $y_t$, we scan the three-dimensional parameter space formed by the two jumps and the non-minimal coupling $\xi$. The spectral index $n_s$ can take any value in the observationally allowed range. The lower limit for the running is $\alpha_s>-3.5\times10^{-3}$, and $\alpha_s$ can be as large as the observational upper limit. Running of the running is small. The tensor-to-scalar ratio is $2.2\times 10^{-17}<r<2\times10^{-5}$. We find that slow-roll can be violated near the feature, and a possible period of ultra-slow-roll contributes to the widening of the range of CMB predictions. Nevertheless, for the simplest tree-level action, the Palatini formulation remains distinguishable from the metric formulation even when quantum corrections are taken into account, because of the small tensor-to-scalar ratio.